What is Nonalcoholic Fatty Liver Disease?

Nonalcoholic fatty liver disease, or NAFLD, occurs when fat builds up in the liver of someone who drinks little or no alcohol. It is the most common liver disease in the world, and for most people it causes no symptoms at all until it is well advanced.

You may also see it called MASLD, metabolic dysfunction-associated steatotic liver disease. In 2023 an international consensus of liver societies renamed NAFLD to MASLD, and its more serious form NASH to MASH, because the words nonalcoholic and fatty were considered imprecise and stigmatising, and because the new name points at the actual cause: metabolic dysfunction. Nothing about diagnosis or treatment changed with the name. We use both terms here because you will encounter both.

Nonalcoholic Fatty Liver Disease Symptoms

This is the difficult part: usually there are none. NAFLD is typically silent, which is why it is so often found by accident.

When symptoms do appear they are easy to dismiss. Fatigue, a general sense of being unwell, and discomfort or a dull ache in the upper right side of the abdomen are the most common. In advanced disease, when cirrhosis has developed, you may see jaundice, swelling in the abdomen or legs, easy bruising and confusion.

The Four Stages

Steatosis, or simple fatty liver, is fat accumulating with no inflammation or scarring. No symptoms.

NASH (MASH) is the more serious stage, where fat build-up has caused inflammation and liver cell damage.

Fibrosis develops as the liver repairs that damage and leaves scar tissue behind. The liver still works at this stage.

Cirrhosis is the most severe stage, where scar tissue has replaced enough normal liver that function is impaired. Damage at this point is largely permanent, though removing the cause prevents further progression.

Can Nonalcoholic Fatty Liver Disease Be Reversed?

Yes, in its earlier stages, and the amount of weight loss required is unusually well defined.

A landmark study published in Gastroenterology followed nearly 300 patients through a year of lifestyle change, with liver biopsies before and after. Losing at least 5 percent of body weight improved fatty deposits in the liver. Losing at least 7 percent was associated with resolution of the inflammatory form of the disease. Losing at least 10 percent was associated with regression of existing scarring, the outcome that matters most and one long thought to be permanent.

The honest caveat is that sustaining a 10 percent loss is difficult and most people do not reach it. But the direction of travel is clear and it starts well below that threshold. Even modest, sustained weight loss measurably improves the liver. There is no medication that substitutes for this, and no scan that substitutes for it either.

Risk Factors

The main risk factors are obesity, type 2 diabetes, insulin resistance, high blood pressure, and abnormal cholesterol or triglycerides, the cluster often described as metabolic syndrome. The more of these you have, the higher your risk. Polycystic ovary syndrome, hypothyroidism and hypopituitarism are also associated.

Obesity is the dominant factor and it is common: the CDC reports 40.3 percent of American adults had obesity during August 2021 to August 2023, rising to 46.4 percent among adults aged 40 to 59. Family history appears to matter too, though researchers still do not fully understand why fat accumulates in some livers and not others, or why it progresses for some people and not others.

What Imaging Can and Cannot Tell You

MRI is genuinely good at one part of this and genuinely limited at another, and the distinction matters.

A specialised MRI technique called proton density fat fraction, or MRI-PDFF, is considered the most accurate non-invasive way to measure how much fat is in the liver. It produces an actual percentage and is sensitive enough to track whether that percentage falls as you make changes.

What MRI does not do well is detect early scarring. Mild fibrosis is largely invisible on standard anatomical MRI. Picking it up requires a different technique such as MR elastography or FibroScan, which measure how stiff the liver has become, or blood-based scores such as FIB-4. Standard imaging only shows scarring once it is advanced enough to change the liver’s shape, and by then it is no longer mild.

So imaging can tell you fat is present and roughly how much. Determining whether that fat has progressed to inflammation and scarring is a separate assessment your physician should direct, usually starting with blood tests.

Where Our Scan Fits

A whole-body MRI is sensitive to fat in the liver and can show when a liver appears fatty, which is worth knowing given how silent this condition is. You can read more in our health library entry on nonalcoholic fatty liver disease.

Being straight about the trade-off: no radiation, no contrast dye, and a broad look that sometimes finds something meaningful early. Against that, screening scans in people without symptoms frequently turn up incidental findings that prove harmless, and following those up can mean further imaging and a period of real worry. That balance is not the same for everyone, and it is a decision worth making with your physician rather than one we would make for you. It does not replace the tests your doctor already recommends.

If you want a broad structural look, schedule a scan or talk to our team first.

This article is for general education and is not medical advice.